The poem follows the Petrarchan sonnet form rather than the Shakespearean sonnet. In the Petrarchan form, the 14-line poem is presented as a single stanza, though the internal volta or turn is intact and occurs between the octet (eight-line set) and the concluding sestet (six-line stanza). Following the Petrarchan tradition, the rhyme scheme is ABBAABBA CDCDCD. While the poem is in a regular sonnet form, it shows a lurching syncopated feel, mainly because of Milton’s use of enjambment. The rhymes often end on enjambed words, which break up the poem’s flow. Thus, the poem retains an air of unpredictability and violence, despite the formal structure, almost as if its violent subject is bursting out of the enclosed, regular sonnet form. Consider Lines 5-8:

Forget not: in thy book record their groans

Who were thy sheep and in their ancient fold

Slain by the bloody Piemontese that roll’d

Mother with infant down the rocks. Their moans

While “Sonnet 18” differs from Shakespearean sonnets, the Petrarchan form resembles the Shakespearean metrically and consists of iambic pentameter, where each line has five metrical feet, and each foot consists of one unstressed syllable followed by one stressed syllable.